If you like getting other things done while your water filters, gravity bags are the way to go. MSR's AutoFlow XL delivers 10L so is great for groups, yet it packs down to the size of a typical competitor's 4L system. When needed, the filter is easy to clean with no tools required. The hose has a water bottle adapter on the end and a clip for controlling flow.

Weight: 340 g
Filter: 0.2 micron hollow fiber
Effective against (99.99%): bacteria, protozoa, particulate  
Output: approx 1.75 L per minute
Filter life: up to 1500 L